Chain ring options for Cannondale 2x10 Hologram SL crank

My current set up in 39/26 with 11/34 in the rear. How would i go about swapping out the 26 for a 24 or 22 tooth ring? I'm in desperate need of a lower granny gear for some very steep climbs. Where can I find a compatible 24 or 22 to swap out with my existing 26? Also, with the front derraileur be able to handle the drop from 39 to 22? What about going with a chain ring smaller than the 39?